You can find work teaching with just a Masters, but unfortunately, you won't be on the "tenure track". Which means you are likely to be relegated to adjunct status and commensurately poor pay.

Nonetheless, I did find teaching adjunctively to be very helpful for my professional development. It gave me the impetus and confidence to develop my own workshops and supervision groups (and I don't have to sit on any academic committees!)

One of the ironies for me has been that a PhD specifically in Art Therapy has rarely even been available. So those who want to teach Art Therapy have to get an advanced degree in some other discipline. I've always had mixed feelings about that. I did hear that there are some new PhD or EdD opportunities for art therapists.